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Naltrexone hydrochloride (naltrexone) is a prescription medication approved by the U.S. Food and Drug Administration (FDA) to block the effects of opioids taken from outside the body. It is used as part of a treatment plan for opioid use disorder.
Naltrexone is a type of medicine called an opioid antagonist. It binds to opioid receptors and can reduce or completely block the effects of opioids.
Doctors prescribe naltrexone when a person with opioid use disorder has been opioid-free long enough to lower the risk of sudden withdrawal. Naltrexone should be used as part of a complete treatment plan, which may include counseling, support, and steps to help the person take the medicine as directed.
Naltrexone is taken as a tablet by mouth.
Treatment usually starts with 25 milligrams by mouth. If no signs of opioid withdrawal occur, the dose may then be increased to 50 milligrams once daily.
In some supervised treatment plans, a healthcare provider may use 50 milligrams every weekday with 100 milligrams on Saturday, 100 milligrams every other day, or 150 milligrams every third day.
This information is based on prescribing information, but your healthcare provider may tailor your treatment plan. Always follow their guidance.
Side effects reported with naltrexone include:
Serious side effects and warnings reported with naltrexone include:
Get medical help right away if you think you are having a serious reaction.
If you or someone you know needs help, you can contact the 988 Suicide & Crisis Lifeline by calling or texting 988 or by using the online chat.
Before starting naltrexone, your doctor may use a urine opioid test or a naloxone challenge test to help check for recent opioid use or opioid dependence. However, no test can completely confirm that a person has been opioid-free long enough.
You should also be opioid-free before starting naltrexone:
Tell your doctor if you have any allergies to naltrexone or any of its ingredients.
Tell your doctor about all medicines you take, including prescription drugs, over-the-counter medicines, vitamins, and herbal supplements. Be sure to tell them about any medicine that contains an opioid.
Before taking naltrexone, tell your doctor if you:
Do not take naltrexone if you:
Naltrexone is also FDA-approved to treat alcohol dependence.
If you miss a dose, contact your doctor and take your next dose as soon as possible.
If you are pregnant, planning to become pregnant, or breastfeeding, talk with your doctor about whether naltrexone is right for you.
These answers are fact-checked by our editorial staff.
How effective is naltrexone for opioid use disorder?
Naltrexone can block the effects of opioids, including the feeling of getting high. A dose of 50 milligrams once daily provides adequate opioid blockade.
The prescribing information also states that higher doses may block opioid effects for longer periods. Double the usual dose may provide blockade for 48 hours, and triple the dose may provide blockade for about 72 hours.
Naltrexone should be used as part of a complete treatment program. Taking the medicine as directed is important. It has not been clearly shown to lower the chance that people will start using opioids again when they take it on their own after detox.
How quickly does naltrexone reach peak levels?
Naltrexone and its main metabolite reach their highest levels in the blood within about one hour after a dose. The prescribing information does not state exactly how soon the opioid-blocking effect begins.
In clinical studies, 50 milligrams of naltrexone blocked the effects of 25 milligrams of heroin given into a vein for as long as 24 hours.
Does naltrexone interact with other medicines?
Naltrexone can affect how some medicines work, especially medicines that contain opioids. Opioid pain medicines, some cough and cold medicines, and some diarrhea medicines may not work as expected while you are taking naltrexone.
Studies of interactions between naltrexone and medicines other than opioids have not been performed, so caution is advised. The safety of taking naltrexone with disulfiram is not known, and taking both is generally not recommended because both may affect the liver. Lethargy (low energy) and somnolence (sleepiness) have also been reported when naltrexone was taken with thioridazine.
Tell your healthcare provider about the medicines you take, especially any medicine that contains an opioid.
On MyOpioidRecoveryTeam, people share their experiences with opioid recovery, get advice, and find support from others who understand.
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